Gravity Separation & Concentration Methods

Gravity Separation & Concentration Methods2017-04-04T06:57:23-04:00
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Sluicing and Amalgamation (2 replies and 1 comment)

Paul Manumbu
2 years ago
Paul Manumbu 2 years ago

first of all I use this opportunity to appreciate all my fellow metallurgists in this forum, you work is excellent, you are helping a number of people! Be grateful

Secondly , am currently involving in small scale gold processing project by amalgamation, the ore assay is 16-30g/t, and be grind to 120micron, the difficulties I face is poor recovery during sluicing and amalgamating, high amount of gold reports to tailings, and the other fail to be amalgamated! The sluicing angle and flowrate are all ok because I had tried to amalgamate other type of ore, the results were fine! Please help me to improve the gold recovery!

Thanks in advance

2 years ago
Hermann 2 years ago
3 likes by Philibert, BAUD and David

Dear Paul,

if you say sluicing and amalgamating, you mean you 1) amalgamate the sluice box gravity concentrate? Or you are 2) amalgamating the whole ground ore on a plate? The first is not necessary because you can upgrade the sluice gravity concentrate without using mercury (and have even better recovery). The second is nonsense and will never give you a good recovery. 

Minus 120µm is tough for a carpet sluice. It works, even down to 30µm, but the operation has to be perfect. You need a wide enough sluice (not more throughput than 1t per m width and hour), frequent clean-ups (no longer than 1hour), good carpets, no riffles. I guess if you grind down to -120µm, some part of the gold might be smaller than 20-30µm. You will not recover much of this on a sluice, no matter how you operate it (same with a plate).

Are you sure that you have to grind it down to -120µm to liberate it?

First thing you have to do is finding out where and how your gold in the tailings is.

The gold lost in the tailings can be either free (and probably too fine or too flaky) or interlocked in quartz, limonite, pyrite, arsenopyrite. If you have pyrite/arsenopyrite or limonite in your tailings, did you check if they contain gold? A sluice cannot recover all of these completely, contrary to a shaking table or a spiral.

If you say it fails to be amalgamated, then the free gold particles are usually dirty (e.g. covered with an iron stain or oil) or your mecury is old and dirty. Or the gold is in the sulfides, so amalgamation will not get it. But as I said before, you dont need mercury. So instead of improving amalgamation you shoud get away from it, and get better results without.

If the gold is not finer than about 30µm, for a small plant without much financial capacity a good set-up is: Crusher-Mill-carpet sluice-shaking table- direct smelting.

A centrifuge behind the sluice might help to improve recovery but often is not necessary. The best mill for a small primary gold plant with a few tons per hour is a roller mill with screen windows. It works like a giant washing pan and holds back most of the gold, so that the sluice does not need to be perfect.

Best regards


2 years ago

Thank you Professor for this great detailed reply. 
Paul, this is a centrifuge like Hermann is referring to.

2 years ago
goldivanti 2 years ago
1 like by Philibert

In small scale mining, or artisanal mining, important is to minimize all expenses. Often electricity is not available, machines are running on diesel or petrol, and the less power is used, the more income may be obtained.

By using Popandson sluice setup one can capture finest small particles.

Once Gold Well sluice start producing, it may be used to capture smallest particles with less efforts, as there are no carpets at all.

And finally there exist other technologies without mechanics that capture fine gold down to 5 micron by using gravitational method, contact me for that purpose and more information, I may direct you to the manufacturer in Oregon.

The whole process may be done without mercury. Hermann mentioned that small particles may be coated with oxides and will not stick to mercury, further, using mercury is usually forbidden by governmental laws, it endangers nature. Overall, one is loosing gold with mercury.

I should know it, as I am handling tailings after processing with mercury, so gold is lost and we can recover 1.2 grams per tonne in a low grade ores, and up to 6 grams from higher grade ores.

Jean Louis


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